Abstract

Objective: To determine the effect of caesarean section on breast milk transfer (BMT) to the normal term infant over the first week
of life.

Method: A sample of 88 healthy nursing mothers who had a normal vaginal delivery, and 97 mothers who had a caesarean section were
recruited from a teaching hospital. Mothers and midwives were instructed to weigh the infants before and after each feed throughout
the study period using calibrated portable electronic scales.

Results: The volume of milk transferred to infants born by caesarean section was significantly less than that transferred to infants
born by normal vaginal delivery on days 2 to 5 (p < 0.05), but by day 6 there was no difference between the two groups (p
= 0.08). The difference could not be explained by any of the maternal and infant variables measured. Birth weight was regained
by day 6 in 40% of infants born vaginally compared with 20% in those born by caesarean section.

Conclusion: There is a lag in the profile of the daily volume of breast milk transferred to infants delivered by caesarean section compared
with those born by normal vaginal delivery. This study also challenges the widely followed schedules of milk volumes considered
to be suitable for the term infant, which appear to be excessive, at least for the first four to five days post partum.

The effect of obstetric procedures on the transfer of breast milk from nursing mothers to their infants is not known. Anecdotal
evidence suggests that variability in breast milk transfer (BMT) is dependent on the mode of delivery of the infant. BMT is
a function of a finely tuned feedback mechanism, which is potentially susceptible to pharmacological, physical, and psychological
manipulations of the mother and/or her infant.

The effect of maternal opioids on newborn motor and respiratory behaviour is well documented. Nissen et al1 have shown a delay in rooting and suckling behaviour in infants whose mothers received one modest dose of intramuscular pethidine
in labour. These initial infant reflexes are considered pivotal in promoting BMT.

The importance of maternal regional anaesthesia on the newborn’s neurobehaviour is difficult to assess. There is no uniform
neurobehavioural assessment tool, and changing anaesthetic protocols make it difficult to compare one study with another and
relate them to continually evolving contemporary practice. Nevertheless, newborn effects have been reported. Scanlon et al,2 using a combination of neurological tests, found that infants whose mothers received a continuous epidural block using lignocaine
had lower motor scores, including rooting behaviour, than infants where a block was not used. This effect persisted for at
least eight hours. However, the use of epidural bupivacaine did not appear to have the same effect in a later study by the
same author.3 Study infants were similar to the non-medicated control group. Yet, using the neonatal behavioural assessment scale, Sepkoski
et al4 found that epidural bupivacaine did affect infant orientation and motor scores, even after confounding variables had been
controlled for.

The effect on BMT after physical or psychological manipulation of the mother-infant pair as a consequence of a caesarean section
is even less well defined. Nissen et al5 found a reduction in the pulsatility profile of oxytocin and less prolactin released during early suckling episodes in mothers
who had an emergency caesarean section compared with those who had a normal vaginal delivery. Oxytocin and prolactin play
an important part in breast milk ejection and milk synthesis respectively.

Thus evidence on the influence of caesarean section on BMT is, at best, indirect. We therefore carried out a comparative study
of directly measured BMT over the first week of life in healthy term infants born by spontaneous normal vaginal delivery (NVD
group) or caesarean section (CS group).

PATIENTS AND METHODS

A sample of healthy nursing mothers and their healthy singleton term infants with birth weight greater than 2800 g was enrolled
immediately after birth. The sample was taken from a metropolitan hospital in South Australia with an inhouse birth rate of
about 2400 a year. The study was carried out between 1998 and 1999. All mothers exclusively breast fed during the course of
the study.

A normal vaginal delivery was defined as being spontaneous onset, unaugmented, without obstetrical intervention, and without
regional anaesthesia, although nitrous oxide and one dose of intramuscular pethidine was available in labour. Caesarean section
was classified as either elective (without labour) or emergency.

Each mother was supplied with a portable Wedderburn electronic scale (Tanita 1581; accuracy ± 5 g) and instructed how to weigh
her infant and record the result in grams. Each scale was calibrated at the start and end of the study. Infants were demand
fed and weighed fully clothed, immediately before and after each suckling episode (breast feed) throughout the six day period
from birth. The difference between the two recordings was calculated by the investigator analysing the data collected in four
hourly epochs from birth. From these weight data, BMT was calculated as ml/kg birth weight/24 h postpartum period. Naked weights
for all infants were recorded at birth and on day 6 (before a feed).

Realistically, some mothers would be unlikely or unable to enter data in the first four hours after birth (epoch 1). In this
case, the value for the first epoch (if it was missing) was to be imputed by averaging the other five epochs of that 24 hour
period.

For days 2–6 (epochs 7–36), any mother who failed to enter data for four or more feeding episodes was excluded from the study.
For the remaining mothers, where data were missing, the value of the missing observation was imputed by averaging the two
adjacent values.

Maternal variables collected included age, parity, previous breast feeding experience, smoking status, socioeconomic profile,
drugs used during labour, and type of anaesthesia (regional or general anaesthetic). Duration of labour and degree of perineal
trauma were recorded for vaginal deliveries. Infant variables included sex, time to first breast feed (0 to < 1 h, 1 to <
4 h, > 4 h after delivery), one and five minute Apgar score, birth weight, and percentage weight change from birth weight
to weight on day 6.

Written informed consent was obtained following guidelines stipulated by the committee on clinical investigations (ethics)
at Flinders Medical Centre.

Statistical analysis

Data were analysed using SPSS version 10 for Windows. A sample size of 60 in each group had a 90% power to detect a difference
in total BMT over the first six days from birth of 60 ml/kg birth weight (the expected difference between the NVD and CS groups)
assuming that the common standard deviation was 100 using a two group t test with a 0.050 two sided significance level. This was based on the volume of breast milk likely to be transferred to a
term infant (600 ml/kg birth weight) over the first six postnatal days.6

Independent samples Student’s t tests were used to assess differences between group means. Analysis of covariance was used to assess differences between
group means after adjustment for potentially confounding variables.

RESULTS

A total of 240 mothers were recruited to the study. Removal of incomplete records left data for 185 mother-infant pairs available
for analysis (77%). This comprised 88 mothers with a normal vaginal delivery and 97 mothers delivered by caesarean section,
of which 45 had an elective and 52 an emergency section.

Twenty six mothers in the NVD group had sufficiently complete information for the first 24 hours, whereas for days 2–6, data
for a further 62 were available (total 88). Twenty three mothers in the CS group had sufficiently complete information for
the first 24 hours, whereas for days 2–6, data for a further 74 were available (total 97).

Of the 97 mothers in the CS group, 91 (94%) had regional anaesthesia, and six had general anaesthesia. Of the former, 41 had
epidural and 50 had spinal blocks.

Except for parity, previous experience of breast feeding, and time from delivery to first breast feed, there were no significant
differences in relevant maternal or infant variables in the NVD and CS groups, as measured by Student’s t test and χ2 test where applicable (table 1).

Student’s t tests showed that, of the two CS groups, emergency CS had a significantly higher mean BMT on day 2 (p = 0.047) and day 4
(p = 0.044). However, the profiles of BMT were very similar and certainly not clinically different. Accordingly, the CS groups
were combined for this study. Student’s t tests also showed that there was no significant difference in BMT between the spinal anaesthesia and the epidural anaesthesia
group.

Table 2 shows the mean BMT for infant-mother pairs in the NVD and CS groups from birth to the end of day 6. For each of the
six days, the mean BMT in the NVD group was consistently greater than the corresponding BMT in the CS group. Student’s t tests showed that the differences were significant for days 2–5. Figure 1 shows these differences and clearly indicates the
lag in BMT seen in the infants born by caesarean section.

Profile of breast milk transfer (BMT) over the first six postnatal days to infants born by caesarean section (CS) or normal
vaginal delivery (NVD).

Analysis of covariance was used to assess the difference between mean BMT on days 1–6 between the NVD and CS groups after
adjustment for breast feeding experience, parity, and time to first breast feed. The results were quite similar, except that
the difference in day 1 means became significant (p = 0.03). Notably, in neither the NVD nor CS group did time to first breast
feed appear to influence total milk volume over the study period.

Birth weight was regained by day 6 in 40% of infants in the NVD group, but by only 20% of those in the CS group (p = 0.003).
This probably reflects the significant difference in total BMT over days 1–6 between the two groups (table 2).

Student’s t test showed that pethidine in labour did not appear to affect BMT for those mothers delivering vaginally.

DISCUSSION

The aim of this study was to investigate a clinical notion held by experienced midwives that lactogenesis is delayed in mothers
delivered by caesarean section.

Lactogenesis was indirectly assessed by weighing the infants immediately before and after suckling on identical calibrated
portable electronic scales. Cognisant of the relative inaccuracy of the scales and the potential error inherent in the two
weighings, we sought to minimise these errors by ensuring a relatively large sample size.

There was the potential for a Hawthorn effect to have taken place—that is, the weighing process may have influenced the amount
of breast milk expressed. However, this effect, if any, might have been to increase or decrease the volume of breast milk
expressed. Regardless, the study was primarily designed to be a comparative study.

The profile of breast milk volumes taken by the infant over the first 6 days of life appears to be much less than artificial
feeding regimens recommended in contemporary neonatal texts. However, the evidence for such regimens appears to be empirical.
Our findings suggest that artificially fed infants are subjected to excessive loads of water and substrate when these feeding
regimens are followed.

Our results show that the volume of breast milk transferred to infants born by caesarean section is less than that transferred
to infants born by normal vaginal delivery over the first 6 days of life. Not only was this statistically significant but
probably clinically significant as indicated by the weight profiles of these two populations over this period. By day 6, only
20% of infants in the CS group had regained their birth weight compared with 40% in the NVD group. However, by day 6 the difference
in BMT between the two groups was smaller and not significant, suggesting that this effect on lactation, or BMT, is transient.

Although it would seem intuitive that labour, previous breast feeding experience, and the timing of the initial suckling contact
could influence BMT throughout this postpartum period, differences in the BMT could not be explained by any of the maternal
and infant variables measured except on the first day when time after delivery to first breast feed had a transient effect.
About 25% of infants in the CS group had not suckled within the first four hours post partum compared with only 3% in the
NVD group. However, this was shown to have little impact on total milk volume over the study period. The study did highlight
the unacceptable delay in initiating the first infant-breast contact, especially in the CS group. This was determined to be
a system problem which has subsequently been addressed.

Unmeasured but potentially confounding variables, such as the effects of maternal perioperative stress, degree of hydration,
blood loss, mobility score, anaesthesia, and postoperative analgesia, on maternal lactation and infant suckling may have contributed
to the observed differences. Further, it could be argued that women requiring caesarean section may be physiologically or
psychologically different from mothers having a normal vaginal delivery. However, information on these potentially confounding
variables was not collected. The effect of general anaesthesia on BMT could not be investigated in this study as almost all
caesarean sections were performed under regional block.

Although this study shows a significant lag in the naturally progressive postpartum BMT profile in term infants delivered
by caesarean section compared with those delivered vaginally without obstetric intervention, it is unlikely that this has
any long term detrimental effect on the child. Furthermore, whether or not this lag in BMT influences long term lactation
is debatable.

Nissen E, Uvnäs-Moberg K, Svensson K, et al. Different patterns of oxytocin, prolactin but not cortisol release during breastfeeding in women delivered by caesarean
section or by the vaginal route. Early Hum Dev1996;45:103–18.